1. Technical Field
The present invention relates to a gas generating device, and particularly to an inflator for inflating an air bag to protect an occupant of a vehicle.
2. Description of the Prior Art
It is well known to protect a vehicle occupant by using an air bag that is inflated when the vehicle encounters sudden deceleration, such as in a collision. The air bag restrains movement of the vehicle occupant during the collision. The air bag is typically inflated by gas generated by activation of gas generating material. The gas generating material is contained in an air bag inflator.
The gas generating material of an air bag inflator can absorb moisture from the air. The performance of the gas generating material upon activation can be adversely affected by the absorption of moisture. Also, if the gas generating material absorbs enough moisture from the air, an undesired chemical reaction can take place between the moisture and the gas generating material and corrosion of metal parts of the inflator can occur.
Accordingly, the gas generating material is commonly enclosed in a hermetically sealed enclosure. The hermetically sealed enclosure prevents large amounts of air, and thus large amounts of moisture in the air, from coming into contact with the gas generating material over the lifetime of the air bag inflator. A hermetic seal may be defined as a seal which has an equivalent helium leak rate of less than 1.times.10.sup.-5 cubic centimeters per second of helium at one atmosphere pressure differential measured at a specified temperature between -50.degree. C. and 110.degree. C.